In order to overcome a limitation in the physical properties of a power device including silicon, a power device including silicon carbide instead of silicon is under development, and particularly, an improvement in the reliability of the gate of a MOSFET including silicon carbide is demanded.
For example, a vertical type power MOSFET including silicon carbide, as disclosed in Patent Document 1, is structured such that a source region is doped with an n-type dopant at a high concentration and is in direct contact with a gate insulating film.
An example of a silicon carbide MOSFET, as in Patent Document 2, is disclosed in which the concentration of an n-type dopant is set lower only in the vicinity of an upper surface of a source region that is in contact with a gate insulating film. In this case, to achieve a successful ohmic contact with the source region doped with the n-type dopant, a source electrode is formed in an area where a trench is engraved.